In the fire bombing systems presently in use, the ground level dispersal patterns of the liquid are non-uniform. The dispersal patterns tend to be of very low wetness level at the outer edges thereof and of very high wetness level at the centre thereof. The patterns which can be achieved by the presently existing apparatus are all excessively wide.
I have found that the above difficulties result from the fact that in the present systems, the load is discharged into the airstream at a very low falling velocity. The drop tanks are located so that their discharge outlet is located at the lowest possible level with respect to the aircraft. Generally, the drop tanks are positioned just inside the aircraft skin. As a result the load initially enters the airstream at zero vertical velocity. Generally, the outlets from the drop tanks are such that the discharging stream has non-vertical velocity factors which also serve to accelerate the errosion of the stream.
I have found that I can obtain an improved ground pattern by reducing the errosion to which the discharging water load is subjected.
For a given flow rate in mass per time unit, if the velocity is low, the cross-sectional area must be high. It follows that in order to discharge a predetermined load at a predetermined rate, the cross-section of the discharging stream must be considerably higher if the velocity of the stream is very low than it need be if the velocity of the stream is relatively higher. Therefore, if a predetermined load of liquid is dropped in the form of a stream from a fire bomber, the cross-sectional area of the discharging stream for a given flow rate may be reduced if the velocity of the falling stream is increased.
I take advantage of this feature by ensuring that the liquid which is discharged into the atmosphere has a greater falling velocity than that previously provided in fire bombers.
In addition, it is well known that streamlining of an airborne object can greatly facilitate the movement of the object through the air. I effectively streamline the discharging stream of liquid by reducing the width of the stream in a direction which extends transversely to the direction of forward movement of the aircraft. Again, this serves to reduce the rate of errosion.
A further feature which contributes to the rapid rate of errosion of falling liquid streams is the entrapment of air in the falling stream. A substantial proportion of this entrapment occurs during the initial acceleration portion of the fall when the velocity of the falling stream is low. By ensuring that the initial velocity of the discharging stream is substantially higher than that previously provided, I reduce the initial entrapment. Furthermore, by shaping the discharge chute through which the falling stream is discharged to correspond to the profile of the free-falling stream, I can minimize air entrapment in the initial acceleration stage.
According to one aspect of the present invention, there is provided in a fire bomber aircraft having a drop tank in which a liquid storage compartment is formed for storing a fire retardent or fire suppresent liquid, said drop tank having an outlet opening for the liquid and closure means for closing the outlet opening, the improvement of an elongated discharge chute having a through passage which has an input end arranged to communicate with the outlet opening of said tank and a discharge end disposed a substantial distance below the input end, said discharge end opening from the aircraft to atmosphere such that upon movement of the closure means to an open position, liquid will flow through the outlet opening to form a falling stream which will accelerate to a substantial velocity before it is discharged through said discharge end to the surrounding atmosphere to thereby reduce the erosion of the body of liquid which is discharged.
According to a further aspect of the present invention, there is provided a method of aerially discharging a fire retardent or suppresent liquid from a drop tank of an airborne aircraft, the drop tank having an outlet opening therefrom and closure means for closing said outlet, comprising the steps of discharging a stream of liquid from the outlet of the drop tank to form a falling stream of liquid, isolating the falling stream of liquid from the air through which the aircraft is flying until the leading end of the falling stream is accelerated to a velocity which is substantially greater than the velocity of the liquid passing through the outlet opening of the drop tank, and thereafter, discharging the falling stream of liquid from the aircraft into the air to allow it to fall to the ground.